HTLV-1 and the host immune system: how the virus disrupts immune regulation, leading to HTLV-1 associated diseases.

Human T-cell leukemia virus type 1 (HTLV-1) was the first retrovirus shown to cause human diseases, such as adult T-cell leukemia (ATL) and HTLV-1 associated myelopathy/tropic spastic paraparesis (HAM/TSP). Despite extensive study for three decades, it remains elusive how HTLV-1 induces these diseases. HTLV-1 mainly infects CD4 T cells, inducing dysregulation of the host immune system. Recent studies have uncovered the mechanisms of differentiation and function of CD4 T cells at the cellular and molecular levels, extending our understanding of the pathological conditions associated with HTLV-1 infection. This review focuses on recent advances in our understanding of the interaction between HTLV-1 and the host immune system, which should provide us a clue to the mechanisms of HTLV-1 mediated pathogenesis.